What is gestational diabetes?

Pregnant women who have never had diabetes before but who have high blood sugar (glucose) levels during pregnancy are said to have Gestational Diabetes Mellitus (GDM). GDM affects about 4% of all pregnant women – about 135,000 cases of gestational diabetes in the United States each year.

We don’t know what causes gestational diabetes, but we have some clues. The placenta supports the baby as it grows. Hormones from the placenta help the baby develop. But these hormones also block the action of the mother’s insulin in her body. This problem is called insulin resistance. Insulin resistance makes it hard for the mother’s body to use insulin. She may need up to three times as much insulin.

Gestational diabetes starts when your body is not able to make and use all the insulin it needs for pregnancy. Without enough insulin, glucose cannot leave the blood and be changed to energy. Glucose builds up in the blood to high levels. This is called hyperglycemia.

Women with gestational diabetes are at risk for complications, such as very large babies, difficult labor and delivery, and stillbirth. Being overweight, being older than 25 years of age, or having family members with diabetes increases a woman’s risk for gestational diabetes. The treatment of gestational diabetes includes a low sugar diet and possibly insulin injections.

Gestational Diabetes Screening

Most medical providers test to check for GDM at around the 24th-28th week of pregnancy, even if a woman has no symptoms or risk factors. Testing people without symptoms is called screening. There are multiple methods for screening for GDM depending on risk factors and results of initial screening tests.


Fasting Blood Glucose or Random Blood Glucose Test
For a fasting blood glucose test, a woman must have nothing to eat or drink except water for at least 8 hours before blood is drawn from her arm to check for blood sugar levels. A random glucose test is one that is checked at any point during the day.

High levels of glucose for either of these tests would not be considered diagnostic of GDM, but would indicate a need for further screening.


Oral Glucose Challenge Test
This test involves quickly drinking a sweetened liquid (called Glucola), which contains 50 g of glucose. The body absorbs this glucose rapidly, causing blood glucose levels to rise within 30 to 60 minutes. A blood sample will be taken from a vein in the arm about 60 minutes after drinking the solution. The blood test measures how the glucose solution was metabolized (processed by the body). If the results are above normal, further tests are recommended.


Oral Glucose Tolerance Test (GTT)

The oral glucose challenge test involves drinking 100 grams of Glucola. Blood glucose levels are then tested four times during a three-hour period. If two out of the four blood tests are abnormal, the woman is considered to have gestational diabetes.


Choosing to Screen

Our practice follows the guidelines of the US Preventative Services Task Force (USPSTF), a group of health experts that reviews published research and makes recommendations about preventive health care.  The USPSTF reviewed the published research to measure the potential benefits and harm of screening for GDM.

USPSTF Patient Summary, 2008

The USPSTF found “that there was not enough information to know whether there are any benefits to screening for gestational diabetes during pregnancy. Treatment of gestational diabetes does reduce a woman’s risk for having a very large baby, but there is not enough information to know whether there are other health benefits.” Many women who are not gestational diabetics have large babies and many large babies are born healthy.

The USPSTF also found information showing “that screening can cause anxiety, but did not find that it causes long-term psychological problems. It also found that most positive screening results are false positive. “False positive” means that, on further testing, the person did not actually have gestational diabetes, so screening may cause unnecessary inconvenience, anxiety, testing, and treatment.”

The USPSTF guidelines for screening recommend “that the choice to screen depends on how a woman and her provider weigh the potential benefits and harms”.  For our practice, this means that we will have a discussion with you about your diet, lifestyle, and hereditary risk factors and determine with you the best choices for GDM prevention.  All screenings are available through our lab account.